of rochester



T. B. DRESCHER BIFOCAL LENS u 9 1 8 .b e F Original Filed March 30 1922 IN V EN TOR. Bflrmdwl.

. the outer surfaces o Reisaued Feb. 9, 1927.

UNITED STATES PATENT orrrce."

THEODORE B. DBESCHER, OF ROCHESTER NEW YORK, ASSIGNOBTO BAU'SOH di LOKB i OPTICAL COMPANY OF ROCHESTER, NEW YOBK, A CORPORATION OF NEW YORK.

IBIFOCAL LENS.

Original No. 1,489,680, dated April 8, 1924, Serial No. 547,957. filed Hatch reissue filed December 27, 1926. Serial No. 157,402.

of two pieces of glass, each having a different index of refraction but both of which have the same relative dispersion.

In carrying out mymvention, Iprefer to employ the well known method of making such lenses with smooth uniform surfaces in which the blank for the major portion adapted for distant vision is provided with a ground and polished recess or countersink in which a minor lens having its convex surface ground and polished to a predetermined contour is secured, referably by fusing, and

the lens are then ground and polished for suitable curves so that the combined effect of the glass and curvature of this minor lens and the glass and curvature of the ma or portion with which it is in contact produce the reading or near vision portion of the lens of greater magnifying power.v

Herctofore in lenses of this class the major and minor portions have been made of crown and flint glass respectively which not only have different refractive in'dices but different relative" dispersions, and the lenses thus produced are objectionable in that with this combination a color or chromatic effect at the margin of the reading portion is so pronounced that many persons are unable to wear them with comfort. On the other hand, if the attempt were made to make both lenses of glass of the same refractive indexthe minor or near vision lensnecessarily of' 'more economically by making the major portion or member of ordinary optical crown ass, but one which will provide countersink,both the major 80, 1922. Application for glass having arefractive index of, for instance, 1.52 and a reciprocal relative dispersion, of say 59% while the minor lens or inserted piece is also of optical crown glass havin a higher index than the former say 1.616, ut the same reciprocal relative dispersion as the major portion. The fusing operations are the same as in the formation of other lenses of this general type, but as the fusing temperatures of both pieces of glass are nearly the same alittle more care isnecessary in preventing too high a fusing tem e'rature so that the ground and polished sur aces will not be deformed.

sectionalview of a bifocal lens constructed in accordance with my invention, 1' representing the major portion and 2 the minor portion or segment.

I claim as m invention: I, 1. A bifocal l ens comprising a major portion for distant vision having a countersink in the lower portion of one of its surfaces,

and asmaller lens segment secured in said countersink, both the major portion and segment being formed of glass relative dispersion but different lndices of refraction. V

2. A bifocal lens comprising a major perso In the accompanying drawing is shown ,a I I aving the same tion for distant vision having a countersink in the lower portion of one of its surfaces and a smaller lens segment secured in said ortion and segment being formed of glass liaving the same relative dispersion but that of the segment havirig a higher index of refraction.

glass and having a countersink in the lower ortion of one of Its, surfaces and a smaller ens segment also composed of crown glass bifocal lens comprising a ma'or por- 1 tion for distant v1s1on composed o crown 

